Electronic systems such as computer systems often use electrical components that operate at different power supply voltage levels. The computer systems are designed to meet industry standards that include standards for bus systems which interconnect the components. One such standard bus system is the peripheral component interconnect (PCI) bus system. The PCI bus system is a high performance bus system which is used to interconnect integrated circuits, printed circuit boards and processor or memory subsystems within a computer. Industry standards are employed for bus systems because they define common form factors, power and voltage requirements and interconnect configurations that enable multiple manufacturers to manufacture components that can connect to the bus system. Computer systems usually include a common backplane that includes slots which provide PCI bus access to printed circuit cards or PCI cards that are inserted into the slots. In accordance with the PCI standards, the slots can accept PCI cards that operate at one of two or more voltage levels and meet maximum power usage requirements.
To meet these power and voltage requirements, many computer systems include power supply systems having distributed power architectures. With distributed architectures, a common AC to DC power supply is used to generate intermediate voltages, and additional DC to DC voltage converters are used to generate final voltages. With the PCI bus, the AC to DC power supply can be used to generate intermediate voltages such as 48 volts or 12 volts, and subsequent DC to DC voltage converters can be used to generate signaling voltages, such as 3.3 volts or 5 volts.
Power supply systems have also used multiple tap transformers to meet the power and voltage requirements. Multiple tap transformers include a number of taps which can provide the needed voltage levels.
One problem is that the maximum power usage is defined for each PCI card, but the specific supply voltage level from which power may be consumed is not. As a result, power supply systems are typically designed to supply the maximum power requirement for each of the final voltage levels which are provided. For an example PCI bus system that can use PCI cards that operate at 3.3 volts or 5 volts, the DC to DC converter providing the 3.3 volts and the DC to DC converter supplying the 5 volts are each able to provide sufficient power for all of the slots in the computer system in case all of the PCI cards are operating at 3.3 volts or at 5 volts.
This unused power supply capacity typically increases manufacturing costs. If power redundancy is employed, the manufacturing costs are further increased, because the redundant power supply system is able to provide twice the amount of power at each signaling voltage level. With large computer systems that include many slots, these manufacturing costs can become substantial.